Start on implementing buying drinks
Update templates to include participant overview.

- Add a menu
- Add additional templates
- Show form in buy menu for debugging
Add debit_id field to store direct debit form related information

- Automatically restarts at 1 for each event
- Automatically increments
Update participant overview to split participants that do have a point of sale account and those that don't

- Split participants and display them in seperate lists
- Add decorators so that login is now required
- Add possibility to create accounts and grant credits
Make login required for overriding registration deadline.